1. Field of the Invention
The present invention pertains broadly to airhouses for supplying conditioned air to the interior of an enclosed building, and more particularly to an improved airhouse compatible with existing systems and having reduced initial cost and increased operating efficiency.
2. Description of the Prior Art
In a system developed in recent years for maintaining desired atmospheric conditions throughout large industrial-type buildings, the building interior is substantially isolated or enclosed and conditioned air, including sufficient outside air, is continuously admitted through air handling units, or airhouses, located about the building to maintain the interior of the building under a slight positive pressure throughout, slightly greater than the effective outside atmospheric pressure are around the building. Various aspects of such a system described, by way of example, in U.S. Pat. Nos. 4,850,264, 4,960,041 and 5,146,977, as well as the above identified copending U.S. patent applications. As discussed at length therein, sensors strategically located throughout the building monitor various atmospheric conditions such as relative interior and exterior atmospheric pressures, temperature, humidity, pollutants of and particulate levels, and transmit signals indicative the readings to a central computer. The computer periodically monitors the signals and compares them to stored data representing desired parameters for the atmospheric conditions in the various zones monitored by the sensors. The controllable airhouses strategically located about the building, generally on the roof, are individually regulated in response to signals from the central computer to collectively take corrective measures when a trend for an atmospheric condition in a particular area to fall outside the predetermined parameter is detected.
Airhouses used heretofore in such systems have generally included a sheet metal cabinet housing a heat source, typically a direct-fired gas burner or steam coil, a fan or blower unit, and a system of dampers for regulating admission of air to and discharge of air from the airhouse. The airhouse might also include evaporative humidification equipment. Such airhouses perform well for their intended purpose. However, they have certain limitations which the present invention overcomes. Thus, the blower of the airhouse has limited capacity so that in order to provide the required volume of air for operating the system, a relatively large number of airhouses is required.
The airhouses are generally installed on the roof of the structure, and installation of each unit requires substantial modification to the roof structure, so that multiplication of the units adds to the overall cost. In addition, the prior art units have a fixed capacity, that is, the blower units operate at a constant velocity to output a constant volume of air. The proportion of outside and building return air is modulated by operating dampers in the outside air and building return air inlets in opposition. In order to provide a straight line variation in damper flow capacity, so that the combined flow of the dampers remains constant, the prior art dampers require a significant area in the airhouse.